1. Field
One embodiment of the invention relates to a magnetic recording medium including magnetic regions that are separated between tracks, and to a magnetic recording apparatus recording information to and reproducing information from the magnetic recording medium.
2. Description of the Related Art
In recent years, there has been a demand for magnetic recording apparatuses, and particularly for magnetic disk apparatuses, to have a high transmission rate and large capacity. With an improvement in the performance of calculators, required performances tend to be improved.
In magnetic recording, in order to improve recording density, it is necessary to form a row of fine magnetic domains in a magnetic recording layer using the magnetic field generated by a recording head. Accordingly, magnetic recording media using an in-plane recording method and a vertical recording method have been researched and developed.
A structure for physically narrowing down a track pitch in a radius direction has been proposed to increase recording density per unit area. In the vertical recording method, it has been checked that a recording density of 100 Gbit/inch ^2 or more is obtained.
FIG. 22 is a cross-sectional view of a conventional magnetic disk apparatus. A magnetic recording medium 10 is attached to a spindle motor 14 through a hub 15, and is rotated at a predetermined angular velocity. The spindle motor 14 is rotated while maintaining a predetermined number of revolutions under the control of a control mechanism 18. A driving mechanism 17 is composed of a voice coil motor (VCM), and rotates a slider having a recording and reproducing head 16 mounted thereon such that the recording and reproducing head 16 is loaded to or unloaded from the magnetic recording medium 10 and seek an inner circumference or an outer circumference. The control mechanism 18 performs servo control on the driving mechanism 17 to control the rotation of the slider having the recording and reproducing head 16 mounted thereon.
In the magnetic recording medium 10, when the track pitch is narrowed, adjacent tracks are written due to a leakage magnetic field generated from a side surface of the magnetic head 16. Accordingly, crosstalk occurs when recorded data is reproduced. In addition, since a bit length is small, the resolution of a recording mark is lowered, which results in the deterioration of signal quality.
In order to prevent the deterioration of signal quality due to an increase in recording density, a discrete track recording method has been proposed. As illustrated in FIG. 23, in the discrete track recording method, in a data region 12 of the magnetic disk 10, a non-magnetic region 13a is formed between adjacent tracks 13b. The data regions 12 are separated from each other with a servo region 11 interposed therebetween in the circumferential direction of the magnetic disk 10, and data can be recorded only on the track 13b made of a magnetic body (for example, see Japanese Patent Application Publication (KOKAI) No. 2005-50482).
On the other hand, a patterned media recording method that isolates magnetic domain particles has been proposed. Instead of forming the track 13b in the data region 12 as a continuous magnetic region, the patterned media recording method forms a single bit pattern, thereby improving recording resolution.
In the magnetic disk apparatus, in order to stably perform recording and reproducing, it is necessary to position the recording and reproducing head 16 over a predetermined track or bit pattern. Therefore, a sector servo method is used. The sector servo method controls the recording and reproducing head 16 to be disposed at an optimal position on the basis of a servo signal written to a servo region 11 that is arranged at a head portion of the data region 12. Since the servo control is intermittently performed on each sector, it is called a sample servo method.
In the conventional continuous recording medium, even when there is a little positional fluctuation in the recording and reproducing head 16 between the sectors or there is a deviation in track servo, it is possible to reduce influence of the fluctuation or the deviation on recording and reproducing characteristics by setting a track pitch with a margin.
However, in the discrete track method or the patterned media method, when the data region is patterned and the gap between adjacent tracks is reduced, the position accuracy of the pattern during the manufacture of a medium, the positional fluctuation of the recording and reproducing head 16, and the track servo deviation exceed their permissible limits.
Therefore, even when appropriate track servo is performed on the servo frame arranged at the head of each sector, it is difficult to perform recording and reproducing at the exact position of the data region.
In the conventional continuous recording medium, a writing is performed at the rising edge of a write gate signal using a servo gate signal indicating the end of the servo region 11 as a base point. In a general format of the data region, a preamble and a sync mark are written at a predetermined time interval by the write gate signal, and a data signal is written. During reading, a reproduction signal is synchronized with the preamble module at the head and the gain of an amplifier is adjusted to recognize a sync mark. Then, signals are read from the data region.
In performing the aforementioned operation by the patterned media recording method, during writing, the bit pattern of the medium needs to be disposed at a write position. As a signal such as the write gate signal, a write clock signal and the bit pattern position are required to be synchronized in time.
A method has been proposed which synchronizes write clock timing with the bit pattern position (for example, see Japanese Patent Application Publication (KOKAI) No. 2006-164349). In the method, recording is performed at certain timing and the error rate of a reproduced signal is examined to determine whether there is an error in the recording. A recording clock is generated on the basis of the determination result, and the phase of a recording is adjusted to the conditions where an optimal error rate is obtained, in order to perform optimal recording.
In a magnetic disk apparatus having a magnetic recording and reproducing head mounted on a swing arm, when recording and reproducing are performed, the positional deviation between a write head and a read head occurs. When the read head is disposed at a specific track, the write head is displaced in the radius direction of the medium, according to the yaw angle of the head. Therefore, it is necessary to perform recording by acquiring positional information (servo information) using the read head and accurately moving the write head by a distance corresponding to the relative position between the write head and the read head to position the write head.
Similarly, the positional deviation between the write head and the read head in the circumferential direction and the radius direction of the medium varies depending on the yaw angle. The positional deviation appears as the deviation between recording timings. Therefore, it is possible to correct the recording timing at each position of the medium in the radius direction.
As such, when the relative positional relationship between the write head and the read head is not accurately checked according to the position of the medium with the yaw angle, it takes long time to examine the recording timing, and the operation time of the apparatus is increased, which results in performance deterioration. The aforementioned conventional technology does not disclose a method of detecting the positional relationship between the write head and the read head.
According to conventional technology, the servo region is patterned to increase recording density. In the patterned media recording method and the discrete track recording method, a servo pattern is formed in the servo region by patterning a magnetic film.
In this case, according to the conventional continuous medium recording method, recording is to be performed by a bipolar magnetic pattern. However, a patterned magnetic film comprises a unipolar magnetization pattern. Therefore, the amplitude of a reproduction signal is reduced by a bipolar magnetization pattern signal, and the transient response (Sag) of the signal occurs due to transition from a bipolar signal of the data region to a unipolar signal of the servo region. Therefore, when the signal is synchronized, the stability of the signal is reduced.
In the patterned medium, the position accuracy of the bit pattern on the medium is likely to be reduced due to manufacturing. In addition, when a circular track having the bit pattern formed therein is eccentrically arranged with respect to the rotation center of a spindle motor (SPM), the radius of rotation varies depending on the amount of eccentricity and a circumferential velocity is changed. As a result, the deviation between the recording and reproducing timings occurs, and a phase difference between the position of the bit pattern on the medium and a recording and reproduction signal clock occurs.